Method and apparatus for measuring and removing rotational variability from a nip pressure profile of a covered roll of a nip press

ABSTRACT

Multiple groups of sensors are circumferentially spaced apart at each cross-directional position along a sensing roll of a nip press to measure and cancel or nearly cancel the effects of rotational variability which may be acting on the sensing roll. The strategically-placed sensors are designed to measure the pressure being placed against the web that is being advanced through the nip press. The average of the measurements of multiple sensors spaced circumferential apart provides a good cancellation of any rotational variability that might be found at a cross-directional position on the sensing roll. In this manner, a more true measurement of the nip pressure profile can be obtained and better adjustments made to reduce nip pressure profile variability. In addition, the nip variability profile may be used as a predictor of cover or bearing failures, resonant frequencies and other roll anomalies.

BACKGROUND OF THE INVENTION

The present invention relates generally to nip presses used to exertpressing forces on moving webs for the formation of, for example, paper,textile material, plastic foil and other related materials. Inparticular, the present invention is directed to methods and apparatusfor measuring and removing the effects of rotational variability fromthe nip pressure profile of nip presses which utilize imbedded sensorsin covered rolls. While prior art presses which utilize rolls withimbedded sensors may be capable of detecting variations in pressurealong the length of the roll, these same imbedded sensors may not becapable of measuring and compensating for rotational variability thatcan be generated by the high speed rotation of the covered roll. Thepresent invention provides a method and apparatus for measuring andremoving rotational variability from the nip pressure profile of thecovered roll so as to obtain a more true profile of the nip pressurebeing developed in the nip region.

Nipped rolls are used in a vast number of continuous process industriesincluding, for example, papermaking, steel making, plastics calenderingand printing. The characteristics of nipped rolls are particularlyimportant in papermaking. In the process of papermaking, many stages arerequired to transform headbox stock into paper. The initial stage is thedeposition of the headbox stock, commonly referred to as “white water,”onto a paper machine forming fabric, commonly referred to as a “wire.”Upon deposition, the a portion of the white water flows through theinterstices of the forming fabric wire leaving a mixture of liquid andfiber thereon. This mixture, referred to in the industry as a “web,” canbe treated by equipment which further reduce the amount of moisturecontent of the finished product. The fabric wire continuously supportsthe fibrous web and advances it through the various dewatering equipmentthat effectively removes the desired amount of liquid from the web.

One of the stages of dewatering is effected by passing the web through apair or more of rotating rolls which form a nip press or series thereof,during which liquid is expelled from the web via the pressure beingapplied by the rotating rolls. The rolls, in exerting force on the weband fabric wire, will cause some liquid to be pressed from the fibrousweb. The web can then be advanced to other presses or dry equipmentwhich further reduce the amount of moisture in the web. The “nip region”is the contact region between two adjacent rolls through which the paperweb passes. One roll of the nip press is typically a hard steel rollwhile the other is constructed from a metallic shell covered by apolymeric cover. However, in some applications both roll may be covered.The amount of liquid to be pressed out of the web is dependent on theamount of pressure being placed on the web as it passes through the nipregion. Later rolls in the process at the machine calender are used tocontrol the caliper and other characteristics of the sheet. Coveredrolls are at times used at the calender. The characteristics of therolls are particularly important in papermaking as the amount ofpressure applied to the web during the nip press stage can be criticalin achieving uniform sheet characteristics.

One common problem associated with such rolls can be the lack ofuniformity in the pressure being distributed along the working length ofthe roll. The pressure that is exerted by the rolls of the nip press isoften referred to as the “nip pressure.” The amount of nip pressureapplied to the web and the size of the nip can be important in achievinguniform sheet characteristics. Even nip pressure along the roll isimportant in papermaking and contributes to moisture content, caliper,sheet strength and surface appearance. For example, a lack of uniformityin the nip pressure can often result in paper of poor quality. Excessivenip pressure can cause crushing or displacement of fibers as well asholes in the resulting paper product. Improvements to nip loading canlead to higher productivity through higher machine speeds and lowerbreakdowns (unplanned downtime).

Conventional rolls for use in a press section may be formed of one ormore layers of material. Roll deflection, commonly due to sag or niploading, can be a source of uneven pressure and/or nip widthdistribution. Worn roll covers may also introduce pressure variations.Rolls have been developed which monitor and compensate for thesedeflections. These rolls generally have a floating shell which surroundsa stationary core. Underneath the floating shell are movable surfaceswhich can be actuated to compensate for uneven nip pressuredistribution.

Previously known techniques for determining the presence of suchdiscrepancies in the nip pressure required the operator to stop the rolland place a long piece of carbon paper or pressure sensitive film in thenip. This procedure is known as taking a “nip impression.” Latertechniques for nip impressions involve using mylar with sensing elementsto electronically record the pressures across the nip. These procedures,although useful, cannot be used while the nip press is in operation.Moreover, temperature, roll speed and other related changes which wouldaffect the uniformity of nip pressure cannot be taken into account.

Accordingly, nip presses were developed over the years to permit theoperator to measure the nip pressure while the rolls were being rotated.One such nip press is described in U.S. Pat. No. 4,509,237. This nippress utilizes a roll that has position sensors to determine an unevendisposition of the roll shell. The signals from the sensors activatesupport or pressure elements underneath the roll shell, to equalize anyuneven positioning that may exist due to pressure variations. Thepressure elements comprise conventional hydrostatic support bearingswhich are supplied by a pressurized oil infeed line. The roll describedin U.S. Pat. No. 4,898,012 similarly attempts to address this problem byincorporating sensors on the roll to determine the nip pressure profileof a press nip. Yet another nip press is disclosed in U.S. Pat. No.4,729,153. This controlled deflection roll further has sensors forregulating roll surface temperature in a narrow band across the rollface. Other controlled deflection rolls such as the one described inU.S. Pat. No. 4,233,011, rely on the thermal expansion properties of theroll material, to achieve proper roll flexure.

Further advancements in nip press technology included the development ofwireless sensors which are imbedded in the sensing roll covers of nippresses as is disclosed in U.S. Pat. Nos. 7,225,688; 7,305,894;7,392,715; 7,581,456 and 7,963,180 to Moore et al. These patents showthe use of numerous sensors imbedded in the roll cover, commonlyreferred to as a “sensing roll,” which send wireless pressure signals toa remote signal receiver. U.S. Pat. No. 5,699,729 to Moschel disclosesthe use of a helical sensor for sensing pressure exhibited on a roll.Paper machine equipment manufacturers and suppliers such as Voith GmbH,Xerium Technologies, Inc. and its subsidiary Stowe have developed nippresses which utilize sensors imbedded within the sensing roll cover.These nip press generally utilize a plurality of sensors connected in asingle spiral wound around the roll cover in a single revolution to forma helical pattern. An individual sensor is designed to extend into thenip region of the nip press as the sensing roll rotates. In thisfashion, the helical pattern of sensors provides a different pressuresignal along the cross-directional region of the nip press to providethe operator with valuable information regarding the pressuredistribution across the nip region, and hence, the pressure that isbeing applied to the moving web as it passes through the nip region.

Control instrumentation associated with the nip press can provide a goodrepresentation of the cross-directional nip pressure (commonly referredto as the “nip pressure profile” or just “nip profile”) and will allowthe operator to correct the nip pressure distribution should it arise.The control instruments usually provide a real time graphical display ofthe nip pressure profile on a computer screen or monitor. The nipprofile is a compilation of pressure data that is being received fromthe sensors located on the sensing roll. It usually graphically showsthe pressure signal in terms of the cross-directional position on thesensing roll. The y-axis usually designates pressure in pounds perlinear inch while the x-axis designates the cross-directional positionon the roll.

While a single line of sensors on the sensing roll may provide a fairlygood representation of nip pressure cross-directional variability, thesesame sensors may not properly take into account the variability ofpressure across the nip region caused by the high speed rotation of thesensing roll. The dynamics of a cylinder/roll rotating at a high angularspeed (high RPMs) can cause slight changes to the pressure produced bythe cylinder/roll that are not necessarily detectable when thecylinder/roll is at rest or rotating at a low speed. Such dynamicchanges could be the result of centrifugal forces acting on thecylinder/roll, roll flexing, roll balance, eccentric shaft mounting orout-or round rolls and could possibly be influenced by environmentalfactors. The dynamic behavior of a typical high speed rotatingcylinder/roll is often characterized by a development of an unbalanceand bending stiffness variation. Such variations along the cylinder/rollare often referred to as rotational variability. Unbalance can beobserved as a vibration component at certain rotating frequencies andalso can cause unwanted bending of the flexible cylinder/roll as afunction of the rotating speed. Since the lengths of the sensing rollsused in paper manufacturing can be quite long, unbalance in the rotatingrolls can pose a serious problem to the paper manufacturer since a lessthan even nip pressure profile may be created and displayed by thecontrol equipment. Any unwanted bending of the sensing roll can, ofcourse, change the amount of pressure being exerted on the web as ittravels through the nip roller. Again, since even nip pressure is highlydesired during paper manufacturing, it would be highly beneficial tocorrectly display the nip pressure profile since any corrects to be madeto the rotating roll based on an inaccurate nip pressure profile couldcertainly exacerbate the problem. A single sensor located at anindividual cross-directional position on the sensing roll may not beable to compensate for the effect of rotational variability at thatsensor's position and may provide less than accurate pressure readings.There are three primary measurements of variability. The true nippressure profile has variability that can be term cross-directionalvariability as it is the variability of average pressure percross-direction position across the nip. Each sensor in a single line ofsensors may have some variability associated with it that may becalculated as the data is collected at high speed. This particularvariability profile represents the variability of the high speedmeasurements at each position in the single line of sensors. Thisvariability contains the variability of other equipment in the papermaking process including the rotational variability of the roll nippedto the sensing roll. The third variability profile is the nip profilevariability of multiple sensors at each cross-directional position ofthe roll. This variability represents the “rotational variability” ofthe sensing roll as it rotates through its plurality or sensingpositions.

One of the problems of rotational variability is the creation of “highspots” and “low stops” at various locations along the sensing roll. Asingle sensor located at a cross-directional position where a high spotor low spot is found could provide the processing equipment with aninaccurate pressure reading being developed at that location. This isdue to the fact that the overall pressure that is developed at thesensor's location as the roll fully rotates through a completerevolution will be lower that the measured “high spot” reading.Accordingly, a nip pressure profile which is based on the reading of asensor located at a high or low spot will not be indicative of theaverage pressure being developed that that location. The processingequipment, in relying on this single, inaccurate reading, will calculateand display a nip pressure profile which is at least partiallyinaccurate. If a number of single sensors are located at numerous highor low spots, then the processing equipment will display a nip pressureprofile which has numerous inaccuracies. The operator of the papermakingmachinery may not even be aware that the processing system is displayingan inaccurate nip pressure profile. Further, attempts to correct thesensing roll based on an inaccurate nip pressure profile could lead toeven greater inaccuracies.

Therefore, it would be beneficial if the manufacturer could detect andmeasure any rotational variability along the length of the covered rollof a nip press and compensate for it when a real time nip pressureprofile is being calculated and displayed. The present inventionprovides a better measurement of the true nip pressure profile and isalso capable of providing a previously unmeasured nip profilevariability of the rotation (rotational variability). Furthermore,certain arrangements of sensing elements will provide information on thewear of the cover. Compensation for any rotational variability shouldproduce a nip pressure profile which is a more accurate representationof the pressure being developed along the nip region of the press. Thepresent inventions satisfy these and other needs.

SUMMARY OF THE INVENTION

The present invention provides apparatus and methods for accuratelydetecting, measuring and at least partially removing any effects ofrotational variability from a covered roll (also referred to as a“sensing roll”) used in nip presses. The present invention compensatesfor this effect allowing a more accurate display of the nip pressureprofile to be calculated and displayed. The present invention thusprovides the machine operator with a more accurate representation of theactual pressure distribution across the nip press. The present inventioncould be used in collaboration with correcting instrumentation which caneliminate or compensate for pressure variability at locations across thesensing roll of the press. The data obtained from the arrangement ofsensors along the sensing roll allows for the calculation and display ofa rotational variability profile which can provide the operator withadditional real time information concerning the dynamics of the pressurereadings in order to obtain a more accurate nip pressure profile. Thepresent invention can compensate for rotational variability in thesensing mechanism by calculating, for example, an average pressure valueat each cross-directional (“CD”) position along the sensing roll. Thepresent invention also could calculate and obtain a more accurate nippressure profile utilizing other models, such as curve fitting.

The present invention uses multiple sensors circumferentially spaced atvarious cross-directional positions along the sensing roll in order tocancel the effects of rotational variability which may, or may not, beacting on the sensing roll. These strategically-placed sensors aredesigned to measure the pressure being placed against the web that isbeing advanced through the nip press. Previous work has demonstratedthat roll rotational variability principally occurs at 1 times therotational frequency of the roll and occasionally at 2 times therotational frequency, primarily near the edges of the roll. Higherfrequencies are rarely seen and then normally only at the extreme edgesof the roll. In additional, cycles at each cross-directional positionmay be in phase where the highs and lows occur simultaneously across theentire roll width (known as “barring”) or the phasing of the highs andlows may vary across the roll as it rotates. Analysis of thesevariability patterns has demonstrated that the average of measurementsof two sensors spaced 180° circumferential apart at a cross-directionalposition of a covered roll should provide a good measurement of theactual pressure being developed and would cancel, or at least partiallycancel, any rotational variability of 1 times the rotational frequencythat might develop at this position. Similarly the average ofmeasurements of three sensors spaced 120° or four sensors spaced 90°circumferential apart at a cross-directional position of a covered rollshould provide a good measurement of the actual pressure being developedand would cancel, or at least partially cancel, any rotationalvariability of 2 times the rotational frequency that might develop atthis position. Alternate positioning of multiple sensors to remove theeffect of rotation is possible. In this manner, a more true measurementof the pressure distribution across the nip region should be obtainable.Information on higher frequency barring which is indicative of coverwear and has been seen at calender stacks may be obtained by spacing thesensing elements at different rotational positions. The differencebetween individual sensing elements and the average of the group ofsensing elements at the same cross-direction progression provides ameasure of the roundness of the roll and shape of the cover. Theprogression of this difference as the cover ages is an indicator ofcover wear.

The present invention provides advantages over sensing rolls and systemwhich utilize a single sensor assigned to measure the pressure at aparticular cross-directional position. Sensing rolls which just utilizea single sensor disposed at a cross-directional position on a roll lackthe ability to take secondary measurements at the same cross-directionalposition for purposes of comparison to determine if there is anyunbalance at that particular cross-directional position. As a result,such a sensing roll may provide inaccurate readings for calculating anddisplaying the nip profile. If the single sensor is placed at a positionwhere there is a high or low spot, caused by rotational imbalance, thenthat sensor's pressure reading will not be quite accurate and itsreading would lead to the calculation of an inaccurate nip pressureprofile. Additionally, the use of single sensors at each CD positioncannot generate the necessary data to allow for the calculation anddisplay of a rotational variability profile which could provide theoperator with additional real time information in order to obtain a moreaccurate nip pressure profile. The present invention allows for thecalculation and display of such a rotational variability profile, alongwith the nip pressure profile.

In one aspect, the sensing roll for use in a nip press includesstrategically-placed sensors including a first set of sensors disposedin a particular configuration along a roll cover that overlies acylindrical member. Each sensor of this first set is located at aparticular lateral position (cross-directional position) on the rollcover. The sensing roll further includes additional sets of sensorswhich are likewise disposed in a particular configuration on the rollcover, each sensor of the second set being likewise disposed at aparticular cross-directional position. Each sensor of the first set ofsensors has a corresponding sensor in the additional sets to define theCD group of sensors that are utilized to take the pressure readings at aparticular cross-directional position. Again, each sensor at thecross-directional position is spaced circumferentially apart from theother. Multiple corresponding sensors can be strategically placed atdifferent cross-directional positions along the length of the sensingroll, each pair of sensors designed to measure the pressure beingdeveloped at that cross-directional position. Each sensor will measurethe pressure as it enters the nip region of the press. In theory, eachcorresponding sensors of a CD group should measure the same pressure atthe particular cross-directional position if the sensing roll is trulybalanced. If the pressure measurements for the two corresponding sensorsare significantly different, then the measurements would indicate somevariability that may be caused by the dynamics of the rotating sensingroll. The present invention allows the sensing roll to take multiple,not just one, pressure measurements at each cross-directional positionduring each 360° revolution of the sensing roll. These multiplemeasurements are utilized to obtain a more accurate nip pressure profileand a rotational variability profile. In one aspect of the invention,the readings at each sensor can be averaged to determine an averagepressure measurement at that particular cross-directional position. Thisaveraged measurement can then be used in computing and displaying thenip pressure profile. The same readings can be used to calculate anddisplay the rotational variability profile of the operating nip press.The variability of the readings at each position will be monitored anddisplayed to determine if the roll rotational variability is stable orincreasing. There are many possible measures of this variabilityincluding variance, standard deviation, 2 sigma, percent of process,co-variance, peak to peak. Increasing variability using any measure maybe indicative of a potential failure in the bearings or roll cover orother roll problems.

In another aspect, multiple sets of sensors are disposed so as aparticular pattern of lined-up sensors are created. For example, thepattern could be a continuous helical configuration which extends aroundthe sensing roll in one revolution forming a helix around the sensingroll. The sensors of several sets can be aligned in a number ofdifferent patterns along the length of the sensing roll in order todevelop a good representative nip pressure profile. In another aspect,the continuous line of sensors can extend only partially around thesensing roll, for example, in one half (½) revolution. A second set ofsensors would also extend around the sensing roll in one half (½)revolution. In this manner, only a partial helix is formed around thesensing roll 10. This arrangement of sensors still allows a pair ofsensors to be assigned to a particular CD position. These sets ofsensors would be spaced 180° circumferential apart from each other. In asimilar manner three helixes may be wound 120° each, four 90° each or nhelixes 360°/n each. The particular advantage of this arrangement ofsensors is in sensing short wavelength bars that may be associated withcover wear as each sensing element is at a different rotationalposition.

In another aspect, a system for calculating and displaying a nippressure profile and rotational variability profile for a nip pressincludes a sensing roll configured with a second roll in a niparrangement, the sensing roll and the second roll adapted to rotatinglypress matter therebetween in a nip region. The sensing roll has aplurality of cross-directional positions defined along its length. Thesensing roll including a first set of pressure-measuring sensors andadditional sets of pressure-measuring sensors, each sensor of the pluralsets of sensors being disposed at a particular cross-directionalposition along the sensing roll. Each sensor is configured to sense andmeasure pressure when the sensor enters the nip region of the nip press.Again, each sensor of the first set has corresponding sensors in theadditional sets which are located at the same cross-directional positionbut are spaced apart circumferentially on the sensing roll to providemultiple pressure readings at each cross-directional position. Theplurality of readings can be used to calculate and formulate the nippressure profile and rotational variability profile for the press. Inone aspect, an average pressure reading at each location can becalculated to obtain a more accurate nip pressure profile.

A transceiver can be attached to the sensing roll and to each of thesensors of the multiple sets for transmitting data signals from thesensors to a receiver unit. A processing unit for calculating the nippressure distribution based on the pressure measurements of each CDgroup of corresponding sensors of the first and additional sets ofsensors can be coupled to the sensing roll. A display unit also could becoupled to the processing unit to provide a visual display of the nippressure profile and the rotational variability profile.

A method for sensing and removing the effects of rotational variabilityfrom the nip pressure profile of a sensing roll of a nip press includesproviding a sensing roll having a working length and a number ofcross-directional positions disposed along the working length. Multiplepressure-measuring sensors are placed at each of the cross-directionalpositions, the sensors of each cross-directional position being spacedapart circumferentially from each other. The pressure being exerted oneach sensor of each CD group as the sensor moves into the nip region ofthe nip press is then measured with the pressure measurements of eachsensor at that cross-directional position being calculate to obtain anaverage pressure measurement at the respective cross-directionalposition. The obtained pressure measurements calculated at eachcross-directional position can then be utilized to create a nip pressureprofile for the nip press.

In yet another aspect, a method for measuring and removing the effectsof rotational variability from the nip pressure profile of a sensingroll of a nip press includes measuring the pressure exerted on a firstsensor disposed at a particular cross-directional position on thesensing roll of the nip press as the first sensor enters the nip regionof the press. The pressure exerted on additional sensors is alsomeasured as the second sensor enters the nip region of the press. Theadditional sensors are located at the same cross-directional position asthe first sensor but spaced apart circumferentially from the firstsensor. The pressure measurements of the multiple sensors are used tocalculate and display the nip pressure profile and rotationalvariability profile. Multiple pluralities of sensors could be placed atvarious cross-directional positions along the sensing roll in order tomeasure pressures at multiple offset locations for eachcross-directional position. The pressure measurements from the multiplesensors for each cross-directional position are averaged and used tocalculate and display the nip pressure profile that is developed acrossthe nip region. The method may include providing corrective proceduresto the sensing roll in order to adjust for high or low pressure spotsalong the nip pressure profile.

These and other advantages of the present invention will become apparentfrom the following detailed description of preferred embodiments which,taken in conjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a nip press which utilizes aparticular embodiment of a sensing or covered roll made in accordancewith the present invention.

FIG. 2 is an end, schematic view of the nip press of FIG. 1 showing theformation of a web nipped between the nip rolls, the nip width of thenip press being designated by the letters

FIG. 3A is a side elevational view of a particular embodiment of asensing roll made in accordance with the present invention which showsthe placement of two sets of sensors along the length of the roll.

FIG. 3B is an end view of the sensing roll of FIG. 3A showing theplacement of the first and second sets of sensors some 180° apartcircumferentially on the sensing roll.

FIG. 4 is a side elevational view showing the placement of the two linesof sensors along the length of the sensing roll with sensors disposedwithin the nip region which is designated by a pair of dotted lines.

FIG. 5 is a side elevational view showing the placement of the two linesof sensors along the length of the sensing roll after the sensing rollhas rotated 180° from its initial position shown in FIG. 4.

FIG. 6A is a side view of a particular embodiment of a sensing roll madein accordance with the present invention which shows the placement ofthree sets of sensors along the length of the roll.

FIG. 6B is an end view of the sensing roll of FIG. 6A showing theplacement of the first, second and third sets of sensors some 120° apartcircumferentially on the sensing roll.

FIG. 7A is a side view of a particular embodiment of a sensing roll madein accordance with the present invention which shows the placement offour sets of sensors along the length of the roll.

FIG. 7B is an end view of the sensing roll of FIG. 7A showing theplacement of the first, second, third and fourth sets of sensors some90° apart circumferentially on the sensing roll.

FIG. 8A is a side view of a particular embodiment of a sensing roll madein accordance with the present invention which shows the placement oftwo sets of sensors wound 180° circumferentially along the length of theroll.

FIG. 8B is an end view of the sensing roll of FIG. 8A showing theplacement of the first and second sets of sensors some 180° apartcircumferentially on the sensing roll.

FIG. 9A is a side view of a particular embodiment of a sensing roll madein accordance with the present invention which shows the placement ofthree sets of sensors wound 120° circumferentially along the length ofthe roll.

FIG. 9B is an end view of the sensing roll of FIG. 9A showing theplacement of the sets of sensors some 120° apart circumferentially onthe sensing roll.

FIG. 10A is a side view of a particular embodiment of a sensing rollmade in accordance with the present invention which shows the placementof four sets of sensors wound 90° circumferentially along the length ofthe roll.

FIG. 10B is an end view of the sensing roll of FIG. 10A showing theplacement of the sets of sensors some 90° apart circumferentially on thesensing roll.

FIG. 11 is a schematic drawing showing the basic architecture of aparticular monitoring system and paper processing line which couldimplement the sensing roll of the present invention.

FIG. 12 is a graphical display showing a plot of normalized error versusprofile position for a single sensor array and two sensor array showinga helical pattern of in-phase variability over one cycle.

FIG. 13 is a graphical display showing a plot of normalized error versusprofile position for a single sensor array and two sensor array (180°)showing a helical pattern of out of phase variability over one cycle.

FIG. 14 is a graphical display showing a plot of normalized error versusprofile position for a single sensor array, a two sensor array (180°)and three sensor array (120°) showing a helical pattern of out of phasevariability over one cycle/rotation center and 2 cycles/rotation edges.

FIG. 15 is a graphical display showing a comparison of nip pressureversus profile position for 3 sensor arrays for array 1 (0°), array 2(90°) and array 3 (180°).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to rolls for use particularly in nippedroll presses, in which rolls exert pressing forces on webs for formingpaper, textile material, plastic foil and other related materials.Although the present invention may be used in the above industries, thediscussion to follow will focus on the function of rolls for useparticularly in the manufacture of paper and particularly to a nip pressfor dewatering a fibrous web, comprising a sensing roll disposed so asto rotatingly cooperate with another roll in the nip press. FIGS. 1-5depict the embodiment wherein two sensors are positioned 180°circumferentially across the width of the roll at each cross-directionallocation as this provides the simplest illustration. Additionalembodiments with multiple sensors at each CD location can beextrapolated, as is shown in FIGS. 6-8B.

As shown in FIG. 1, a schematic perspective view shows a sensing roll 10made in accordance with the present invention as a portion of a nippress 12 which includes a second roll 14 that cooperates with thesensing roll 10 to produce pressure on a fibrous web 16 that is advancedbetween the two rolls 10, 14. The sensing roll 10 and second roll 14rotate, as is indicated by arrows in FIG. 2, and are spaced apart at anip region 18 where the two rolls 10, 14 somewhat meet in order to placepressure on the fibrous web 16 so as to remove some of the liquidsuspended in the web 16. The letters NW in FIG. 2 indicate the formed“nip width” of the nip region 18. This nip region 18 extends along theentire cross-directional length of the sensing roll 10 and second roll14. The sensing roll 10 may include an inner base roll 20 and the outerroll cover 22 may comprise materials suitable for use in making a pressroll. The inner base roll 20 may include one or more lower layers, withthe outer roll cover 22 being the top layer. This composite sensing roll10 with the roll cover 24 is commonly known as a “covered roll” in theindustry. The second roll 14 may be an uncovered roll or also compriseof a number of layers of materials and a base roll as well. If multiplecovered rolls are contained in the nip, each may have sensors andproduce nip profiles and variability profiles. The nip profiles or thetwo covered rolls may be averaged together for greater accuracy inmaking nip profile adjustments. However, the variability profiles ofeach covered roll provide information about the condition of thatspecific roll. It should be appreciated that while the presentembodiments focuses only in a single nip, it is possible to utilizesingle rolls involved in bi-nip, tri-nip or multi-nip interactions whichare common in the paper industry. One two rolls 10, 14 are depicted tomore clearly describe the advantages associated with the presentinvention. However, multiple nip profiles can be generated with eachindependent sensing roll utilizes in the nip press.

Referring now to FIGS. 1 and 3, a first set 24 of sensors 26 isassociated with the sensing roll 10 along with a second set 28 ofsensors 30. Sensors 26 of the first set 24 are designated by a circlewhile sensors 30 of the second set 28 are designated by a square.Circles and squares have been used for ease in identify the sensorsconstituting the first set 24 of sensors from the second set 28 ofsensors. However, in practice, these sensors 26 and 30 can be the exactsame sensing device. Also, one or both of the rolls 10, 14 may havesensors associated with the roll. For purposes of illustration, however,this discussion will focus on only one of the rolls having sensing andmeasuring capabilities.

These sensors 26 and 30 may be at least partially disposed within theroll cover 22 which forms the portion of the sensing roll 10. Each ofthe sensors 26 and 30 are adapted to sense and measure a particular dataparameter, such as, for example, the pressure that is being exerted onthe sensor when it enters the nip region 18. As can be best seen in FIG.3A, the first set 24 of sensors 26 is shown disposed in a particularconfiguration along the sensing roll 10, each sensor 26 being located ata particular lateral position (referred to as the “cross-directionalposition” or “CD position”) on the sensing roll 10. Eachcross-directional position is a particular distance from the first end32 of the sensing roll 10. As can be seen in the particular embodimentof FIG. 3A, the first set 24 of sensors 26 are disposed along a linethat spirals around the entire length of the sensing roll in a singlerevolution forming a helix or helical pattern. The second set 28 ofsensors 30 is likewise disposed along a line that spirals around theentire length of the sensing roll in a single revolution creating thesame helix or helical pattern except that this second set 28 of sensors30 is separated apart from the first set 24 some 180° circumferentiallyaround the sensing roll 10. FIG. 3B shows an end view of the first set24 spaced approximately 180° apart from the second set 28. The use ofthese two lines of sensors 26, 30 allows a large amount of the outersurface of the sensing roll 10 to be measured while the roll 10 isrotating. While the particular pattern of the first set 24 and secondset 28 is shown herein in a helical pattern around the roll 10, itshould be appreciated that these sets 24, 28 of sensors can be disposedin other particular configurations to provide pressure measurements allalong the sensing roll 10.

Each sensor 30 of this second set 28 is disposed at a particularcross-directional position on the sensing roll 10. Each sensor 26 of thefirst set 24 has a corresponding sensor in the second set 28 with eachcorresponding sensor of the first and second set being located at thesame cross-directional position along the sensing roll. In this manner,each cross-directional position of the sensing roll has a pair ofsensors which measure the pressure at two different circumferentialpositions. Each pair of corresponding sensors are located along thesensing roll 10 at a cross-directional position to provide two sensorreadings when the sensing roll completes a full 360° rotation. Theaverage of these two readings can then be utilized to calculate anddisplay the nip pressure profile that is being developed on the rotatingnip press 12.

The manner in which the pressure measurements can be made is bestexplained by referring to FIGS. 4 and 5. FIGS. 4 and 5 show sideelevational views of the sensing roll 10 as it would be viewed lookingdirectly into the nip region 18 which is depicted by a pair of dottedlines. FIG. 4 shows a typical view in which the sensing roll 10 has apair of sensors 26, 30 directly in the nip region ready to take apressure measurement. A grid located at the bottom of the sensing roll10 for illustrative purposes shows fourteen (14) individualcross-directional positions along the working length L of the sensingroll 10. In FIG. 4, the first set 24 of sensors 26 can be seen depictedpositioned at cross-directional positions numbered 1-7. Likewise, thesecond set 28 of sensors 30 are shown in cross-directional positionsnumbered 8-14 in FIG. 4. The other sensor 26 of the first set 24 aredisposed in cross-directional positions 8-14 but cannot be seen in FIG.4. Likewise, the remaining sensors 30 of the second set 28 are inpositions 1-7 but cannot be seen in FIG. 4 since they are at the reverseside of the sensing roll. It should be appreciated that only fourteencross-directional positions are shown in these drawings to provide asimple explanation of the manner in which the present inventionoperates. In actual operation, there can be many more cross-directionalpositional positions associated with a sensing roll given the longlengths and widths that are associated with these rolls.

Only the sensor 26 located in the 4^(th) cross-directional position andthe sensor 30 located in the 11th cross-directional position are inproper position for taking the pressure measurement as they are locatedin the nip region NR. Once these two sensors 26, 30 enter the nip regionNR, the pressure being exerted on the sensor is measured. As the sensingroll 10 continues to rotate, the other sensors in the 5^(th) and 12^(th)cross-directional positions will then be located in the nip region NRand will be able to measure the pressure at these particular positions.Further rotation of the sensing roll 10 places the sensors in the 6^(th)and 13^(th) cross-directional positions into the nip region NR forpressure measurements. Eventually, the sensing roll 10 rotates 180° fromits initial position shown in FIG. 4 and will again have sensors in the4^(th) and 11^(th) cross-directional positions. This arrangement ofsensors 26, 30 is shown in FIG. 5. The only difference is that a sensor30 of the second set 28 is now in the 4^(th) cross-directional positionand a sensor 26 of the first set 24 is in the 11^(th) cross-directionalposition. These sensors 26 and 30 shown in FIGS. 4 and 5 arecorresponding sensors which read the pressure at the 4^(th)cross-directional position. Likewise, sensor 26 of the first set 24 inFIG. 5 is now in the 11^(th) cross-directional position ready to measurethe pressure at that location. The sensor 30 in the 11^(th)cross-directional position shown in FIG. 4 and the sensor 26 in the11^(th) cross-directional position of FIG. 5 constitute correspondingsensors which provide pressure readings at that particular location onthe sensing roll. The system which processes the pressure measurementscan take the average of the readings of each pair of correspondingsensors at a particular cross-directional position and calculate the nipprofile at that position based on an average reading. For example, ifthe sensors 26, 30 in the 4^(th) cross-directional position both read200 lbs per linear inch (PLI) then their average would be 200 PLI. Thiswould indicate that there is little, or no, pressure variation caused bythe rotation of the sensing roll 10. The average 200 PLI reading wouldthen be used to calculate and display the nip pressure profile at thatparticular cross-directional position. For example, if the sensor 30 inthe 11 ^(th) cross-directional position, as shown in FIG. 4, reads 240PLI and the sensor 26 in the 11^(th) position shown in FIG. 5 reads 160PLI, then the average pressure would be 200 PLI. These two differentreadings at the 11^(th) cross-directional position would indicate apressure variation that most likely would be attributed to the highspeed rotation of the sensing roll 10. However, in processing the nippressure profile for the 11^(th) cross-directional position, the averagepressure measurement of 200 PLI would be utilized since this averagewill cancel, or nearly cancel, the effect of rotational variability thatis occurring along the sensing roll 10. The average of the twomeasurements will result in a more accurate representation of thepressure being developed at that particular cross-directional position.

In prior art sensing rolls which utilize a single sensor at eachcross-directional position, the processing unit would have singlesensors at each cross-directional positions. A prior art sensing rollwhich has a single sensor at the 11^(th) cross-directional position inthe illustrated example above could only rely on a single reading atthat position in order to calculate and display the nip pressureprofile. A prior art roll would then use either the 240 PLI or 160 PLIreading for determining and displaying the nip pressure profile at thislocation. Such a reading would be less than accurate as the sensing rollfull rotates in a 360° revolution. Accordingly, the calculated nippressure at this position will be less than accurate. However, theprocessing unit would display a nip pressure profile would appear to beaccurate but in reality would be less than accurate. If adjustments aremade to the sensing roll by the machine operator or through automaticadjustment equipment to compensate for high or low pressure readings,then the sensing roll could be adjusted to develop even more incorrectpressures at various locations in the nip region.

As the roll 10 rotates placing different sensors into the nip region,the respective sensors measure the pressure which is then transmitted tothe processing unit. The processing unit associated with each sensingroll 10 can then calculate the average pressure of each pair ofcorresponding sensors at the various cross-directional positions andproduce a nip pressure profile which can be visualized on a monitor orother visual screen. Computer equipment well known in the art could beutilized to process the pressure readings that are being made inmilliseconds.

One method of the present invention for sensing and removing the effectsof rotational variability from the nip pressure profile of a sensingroll of a nip press thus includes providing a sensing roll having aworking length and a plurality of cross-directional positions disposedalong the working length and the placement of pairs ofpressure-measuring sensors at each cross-directional positions. In theparticular embodiment shown in FIGS. 3A-5, the method utilizes sensorsbeing spaced apart 180° circumferentially from each other. This allowsfor two different pressure measurements to be made at eachcross-directional position. The pressure exerted on each sensor of eachpair as the sensor moves into the nip region of the nip press can thenbe measured and the average of each of the two sensors at eachcross-directional position can be calculated to determine an averagepressure measurement. The average pressure measurements at eachcross-directional position can then be used to provide a nip pressureprofile for the nip press.

It should be appreciated that while the present invention disclosesmathematical modeling that utilizes the direct averaging of themeasurements taken by each corresponding sensor, it could be possible toobtain a composite average measurement utilizing other types of modelswhich can obtain and calculate an averaged measurement at eachcross-directional position. For example, the operating equipment (dataprocessors) could utilize another model such as “curve fitting” whichalso can provide the more accurate nip pressure profile. Still othermodels known in the art could be utilized with the multiple pressurereadings from the various sensors to obtain the more accurate nippressure profile.

Variations of the sensing roll are disclosed in FIGS. 6-8. Referringinitially to FIGS. 6A and 6B, three different sets of sensors areutilized and extend around the sensing roll 10. As can be seen in thedisclosed embodiment of the sensing roll 10, a first set 24 of sensors26, a second set 28 of sensors 30 and a third set 32 of sensors 34 areshown as continuous lines of sensors which extend around the sensingroll in one full revolution, each set 24, 28, 32 forming a helix aroundthe sensing roll 10. Sensors 34 are shown as a triangle to distinguishthat particular sensor from the sensors 26, 30 of the other two sets 24,28. Adjacent sets 24, 28 and 30 of sensors are spaced 120°circumferential apart from each other (see FIG. 6B) at across-directional position of the sensing roll 10 to provide a goodmeasurement of the actual pressure being developed and would cancel, orat least partially cancel, any rotational variability of 2 times therotational frequency that might develop at this CD position. Again, themeasurements from each of the corresponding sensors at each CD positioncan be averaged to provide an averaged measurement which provides a moreaccurate representation of the nip pressure being developed at that CDposition.

It should be appreciated that the working length of the sensing roll canbe quite long and may require each set of sensors to be wound more thanone times around the roll. Again, such a pattern is satisfactory as longas the pattern allows for three sensors to be use at eachcross-directional position (spaced 120° apart) in order to produce threeseparate pressure readings which are then processed to produce a basereading.

Referring now to FIGS. 7A and 7B, a fourth set 36 of sensors 38 has beenadded to the sensing roll 10 to provide yet another sensor at each CDposition. Adjacent sets 24, 28, 30, 36 are spaced 90° circumferentialapart from each other (see FIG. 7B) at a cross-directional position ofthe sensing roll 10 to provide a good measurement of the actual pressurebeing developed and would cancel, or at least partially cancel, anyrotational variability of 2 times the rotational frequency that mightdevelop at this CD position. Again, It should be appreciated that theworking length of the sensing roll can be quite long and may requireeach set of sensors to be wound more than one times around the roll.Such a pattern is satisfactory as long as the pattern allows for foursensors to be use at each cross-directional position (spaced 90° apart)in order to produce four separate pressure readings which are thenprocessed to produce a base reading.

Referring now to FIGS. 8A and 8B, a first set 24 of sensors 26 is shownas a continuous line of sensors which extend around the sensing roll inone half (½) revolution. Likewise, a second set 28 of sensors 30 extendaround the sensing roll in one half (½) revolution. In this manner, onlya partial helix is formed around the sensing roll 10. This arrangementof sensors 26, 30 still allows a pair of sensors to be assigned to aparticular CD position. Like the sensing roll 10 shown in FIGS. 3A-5,adjacent sets 24, 28 are spaced 180° circumferential apart from eachother (see FIG. 8B). The resulting structure creates a sensing roll thathas only one sensor entering the nip region at any given time. Thisparticular embodiment of the sensing roll 10 should provide a goodmeasurement of the actual pressure being developed and would cancel, orat least partially cancel, any rotational variability of 2 times therotational frequency that might develop at this CD position.

In a similar manner three helixes may be wound 120° each, four 90° eachor n helixes 360°/n each. The particular advantage of this arrangementof sensors is in sensing short wavelength bars that may be associatedwith cover wear as each sensing element is at a different rotationalposition. FIGS. 9A and 9B show three continuous lines 24, 28 and 32 ofsensors 26, 30 and 34 which extend around the sensing roll in a partialrevolution (a 120° revolution). In this manner, only a partial helix isformed around the sensing roll 10 by each set 24, 28 and 32. Thisarrangement of sensors 26, 30 and 34 allows group of sensors to beassigned to a particular CD position. Like the sensing roll 10 shown inFIGS. 6A and 6B, adjacent sets 24, 28 and 32 are spaced 120°circumferential apart from each other along the roll (see FIG. 9B).FIGS. 10A and 10B show four continuous lines 24, 28, 32 and 36 ofsensors 26, 30, 34 and 38 which extend around the sensing roll in apartial revolution (a 90° revolution). Again, only a partial helix isformed around the sensing roll 10 by each set 24, 28, 32 and 36. Thisarrangement of sensors 26, 30, 34 and 38 allows group of sensors to beassigned to a particular CD position. Like the sensing roll 10 shown inFIGS. 7A and 7B, adjacent sets 24, 28, 32 and 36 are spaced 90°circumferential apart from each other (see FIG. 10B). The resultingstructure creates a sensing roll that has only one sensor entering thenip region at any given time. This particular embodiment of the sensingroll 10 should provide a good measurement of the actual pressure beingdeveloped and would cancel, or at least partially cancel, any rotationalvariability of 2 times the rotational frequency that might develop atthis CD position. Similar lines of sensors could be disposed along thelength of the sensing roll 10 such that n lines of sensors formingpartial helixes are formed and placed 360°/n along the length of theroll 10. Adjacent lines of sensors would be spaced 360°/ncircumferentially apart from each other along the roll.

The methods for sensing and removing the effects of rotationalvariability from the nip pressure profile of a sensing roll of a nippress utilizing the embodiments of FIGS. 6A-10B includes providing asensing roll having a working length and a plurality ofcross-directional positions disposed along the working length and theplacement of pairs of pressure-measuring sensors at eachcross-directional positions. The method will calculate an averagepressure measurement utilizing the number of sensors placed at each CDposition. In the embodiments of FIGS. 6A and 6B and FIGS. 9A and 9B,three sensors located a CD position are averaged. Likewise, the readingsfrom the four sensors of the embodiments of FIGS. 7A and 7B and FIGS.10A and 10B are utilized to produce an average pressure measurement. Theembodiment of FIGS. 8A and 8B, like the embodiment of FIGS. 3A-5,utilize a pair of sensor measurements at each CD position. The averagepressure measurements at each cross-directional position can then beused to provide a nip pressure profile for the nip press.

The sensors used in the various sets can be electrically connected to atransmitter unit 40 which also can be attached to the sensing unit 10.The transmitter unit 40 can transmit wireless signals which can bereceived by a wireless receiver located at a remote location. Thewireless receiver can be a part of a system which processes the signals,creates the nip profile and sends corrective signals back to the sensingroll 10. Sensors may be collected in the same collection period andaverage together for immediate use. However, the additional wirelesstransmission may reduce the battery life of the wireless unit. As therotational variability changes slowly, alternating the collectionbetween the sensors and averaging together the collections in thealternate collection periods will provide comparable information and maysave battery life.

One particular system for processing the signals is shown in FIG. 11 andwill be discussed in greater detail below. Wireless transmission can becarried out via radio waves, optical waves, or other known remotetransmission methods. If a direct wired transmission is desired, slipring assemblies and other well-known electrical coupling devices (notshown) could be utilized.

FIG. 11 illustrates the overall architecture of one particular systemfor monitoring of a product quality variable as applied to paperproduction. The system shown in FIG. 11 includes processing equipmentwhich calculates and displays the nip pressure profile. For example, thepressure measurements can be sent to the wireless received from thetransmitter(s) located on the sensing roll. The signals are then sent tothe high resolution signal processor to allow the average pressuremeasurements to be calculated and utilized to create and display the nippressure profile. Data can be transferred to the process control whichcan, for example, send signals back to the sensing roll to correctpressure distribution across the nip region. One such nip press which iscapable of real time correction is described in U.S. Pat. No. 4,509,237,incorporated herein by reference in its entirety. This nip pressutilizes a roll that has position sensors to determine an unevendisposition of the roll shell. The signals from the sensors activatesupport or pressure elements underneath the roll shell, to equalize anyuneven positioning that may exist due to pressure variations. Otherknown equipment which can correct the roll cover could also be used.

The sensors can take any form recognized by those skilled in the art asbeing suitable for detecting and measuring pressure. Pressure sensorsmay include piezoelectric sensors, piezoresistive sensors, forcesensitive resistors (FSRs), fiber optic sensors, strain gage based loadcells, and capacitive sensors. The invention is not to be limited to theabove-named sensors and may include other pressure sensors known tothose of ordinary skill in the art. It should be appreciated that datarelating to the operational parameter of interest, other than pressure,could be utilized with the present invention. In this case, the sensorscould be used to measure temperature, strain, moisture, nip width, etc.The sensors would be strategically located along the sensing roll asdescribed above. Depending on the type of sensor, additional electronicsmay be required at each sensor location. The design and operation of theabove sensors are well known in the art and need not be discussedfurther herein.

The processor unit is typically a personal computer or similar dataexchange device, such as the distributive control system of a paper millthat can process signals from the sensors into useful, easily understoodinformation from a remote location. Suitable exemplary processing unitsare discussed in U.S. Pat. Nos. 5,562,027 and 6,568,285 to Moore, thedisclosures of which are hereby incorporated herein in their entireties.

Referring now to FIGS. 12-15, graphical displays are provided whichfurther explains and presents typical mapping of roll variability whichcan develop during operation. Roll surfaces were mapped pursuant to themethods and apparatus described in U.S. Pat. No. 5,960,374 using paperproperties sensors that were related to nip pressure. The mappings usedan array of 5,000 elements broken into 100 CD positions and 50rotational positions. The mappings confirmed that most roll variabilityoccurs in 1 cycle per revolution in-phase across the roll orout-of-phase (the phase shifts with profile position). A 2 cycle perrevolution pattern is sometime noted at the edges of the roll. Higherfrequencies (such as 3 cycles per revolution) are rarely seen and thenonly at the extreme edges and have little impact. Three roll surfacemaps were normalized (scaled on 0-100%) and helical scan paths weresuperimposed over the surface maps. The true nip pressure profile wasdetermined by averaging the 50 rotational positions at each of the 100CD positions. The helical scan paths and the averages of two or more ofthese paths at various separation angles were used to develop estimatesof the nip pressure profile. These estimates were then subtracted fromthe true nip profile to obtain the error in each estimate. FIGS. 12 and13 demonstrate that two sensor arrays across the width of the roll andseparated by 180° circumferentially are sufficient to remove most of therotational variability when the variability is 1 cycle per revolution.FIG. 14 demonstrates that 2 arrays are not sufficient to handle the 2cycle per revolution variability at the edges as the estimate differencefrom the true nip profile is an large at the edges as the single helicalscan. For this case a minimum of 3 arrays separated by 120° would beneeded. A larger number of arrays per revolution may further reduce themeasurement error, but at a higher cost. Therefore, the embodiment ofthree (3) arrays (lines) of sensors separated by 120° circumferentiallyinsures that all 1 cycle/revolution and 2 cycle/revolution variabilityis reduced. However, 2 arrays may be sufficient for many rolls without 2cycle/revolution variability and more than 3 arrays may give superiorvariability measurement and reduction but at a higher cost.

FIG. 15 shows nip pressure profiles collected on a roll using thevarious embedded sensors. The data show clear differences in the profilebetween the 3 arrays. Most notably, arrays 1 & 3 (separated by 180°)show a significant difference in shape, especially in profile position14-20.

While there have been described herein what are considered to bepreferred and exemplary embodiments of the present invention, othermodifications of the invention shall be apparent to those skilled in theart from the teachings herein and, it is therefore, desired to besecured in the appended claims all such modifications as fall within thetrue spirit and scope of the invention. Thus, any modification of theshape, configuration and composition of the elements comprising theinvention is within the scope of the present invention. Accordingly,what is desired to be secured by Letters Patent of the United States isthe invention as defined and differentiated in the following claims.

What is claimed:
 1. A sensing roll for use in a nip press, comprising: asubstantially cylindrical member having an outer surface and adapted forrotational movement; a roll cover circumferentially overlying the outersurface of the cylindrical member; and a sensing system associated withthe roll cover, comprising: a first set of pressure-measuring sensorsdisposed in a particular configuration along the roll cover, each sensorof the first set being located at a particular cross-directionalposition on the roll cover; and at least one additional set ofpressure-measuring sensors disposed in a particular configuration alongthe roll cover, each sensor of the second set being located at aparticular cross-directional position on the roll cover, wherein eachsensor of the first set has a corresponding sensor in the second setwhich is located at the same cross-directional position but is spacedapart circumferentially in an evenly spaced or unevenly spaced manner.2. The sensing roll of claim 1, wherein the first set of sensors arealigned in a helical configuration around the cylindrical member.
 3. Thesensing roll of claim 2, wherein multiple sets of sensors are aligned ina helical configuration around the cylindrical member.
 4. The sensingroll of claim 1, wherein the first set of sensors is aligned around thecircumference of the cover roll in a single revolution.
 5. The sensingroll of claim 4, wherein multiple sets of sensors are aligned around thecircumference of the cover roll in a single revolution.
 6. A sensingroll of claim 5, where the multiple sets of multiple sensors are locatedat each cross-directional position, separated circumferentially in aneven spaced or unevenly spaced manner.
 7. The sensing roll of claim 1,including a transceiver attached to the cylindrical member and each ofthe sensors of the plurality of sets for transmitting data signals fromthe sensors.
 8. The sensing roll of claim 1, wherein the pressure beingapplied to a sensor from the plurality of sets of sensors is measuredwhen these sensors enter the nip region of the nip press.
 9. The sensingroll of claim 1, wherein the at least one additional set ofpressure-measuring sensors includes a second set and a third set,wherein each sensor of the first set has a corresponding sensor in thesecond and third sets which is located at the same cross sectionalposition but is spaced 120° apart circumferentially.
 10. The sensingroll of claim 1, wherein the at least one additional set ofpressure-measuring sensors includes a second set, wherein each sensor ofthe first set has a corresponding sensor in the second set which islocated at the same cross sectional position but is spaced 180° apartcircumferentially.
 11. The sensing roll of claim 1, wherein the at leastone additional set of pressure-measuring sensors includes a second set,a third set and a fourth set, wherein each sensor of the first set has acorresponding sensor in the second, third and fourth sets, eachcorresponding sensor being located at the same cross sectional positionbut is spaced 90° apart circumferentially from an adjacent sensor.
 12. Asystem for calculating and displaying a nip pressure profile for a nippress, comprising: a sensing roll configured with a second roll in a nippress, the sensing roll and the second roll adapted to rotatingly pressmatter therebetween in a nip region, the sensing roll having a pluralityof cross-directional positions along its length, the sensing rollincluding a plurality of sets of pressure-measuring sensors, each sensorof the plurality of sets of sensors being disposed at across-directional position along the sensing roll, each sensorconfigured to sense and measure pressure when the sensor enters the nipregion of the nip press, wherein each sensor of the plurality of setshas a corresponding sensor in each of other sets which is located at thesame cross-directional position but is spaced apart circumferentially onthe sensing roll, each of the corresponding sensors of the plurality ofsets providing a measurement of pressure at the respectivecross-directional position which is averaged to supply an averagemeasurement to processing equipment which calculates and displays a nippressure profile for the nip press and a nip rotational variabilityprofile.
 13. The system of claim 12 wherein a mathematical model is usedto analyze the plurality of sensor readings at each cross-directionalposition to correct the nip pressure and calculate the nip rotationalvariability profile.
 14. The system of claim 12, further including atransceiver attached to the sensing roll and to each of the sensors ofthe plurality of sets for transmitting data signals from the sensors toa receiver unit.
 15. The system of claim 14, further including aprocessing unit for calculating the nip pressure distribution based onthe average of the pressure measurements of each plurality ofcorresponding sensors of the multiple sets of sensors and displaying thenip pressure profile and nip variability profile on a display unit. 16.The system of claim 12, wherein the sensors of the each set are disposedin a certain pattern along the sensing roll.
 17. The system of claim 16,wherein each of the plurality of sets of sensors is disposed in acontinuous helical configuration around the sensing roll.
 18. A methodfor sensing and removing the effects of rotational variability from thenip pressure profile of a sensing roll of a nip press, comprising:measuring the pressure exerted on a first sensor disposed at aparticular cross-directional position on the sensing roll as the firstsensor enters the nip region of the nip press; measuring the pressureexerted on additional sensors at the same cross-directional locations asthey enter the nip region of the press, the additional sensors beinglocated at the same cross-directional position as the first sensor butspaced apart circumferentially from the first sensor; and averaging thepressure measurement of the first sensor and the pressure measurement ofthe additional sensors and determining the nip variability profile. 19.The method of claim 18, further including: displaying the nip pressureprofile based on the calculated average pressure measurements of thefirst and second sensors.
 20. The method of claim 18, further including:displaying the nip pressure profile and nip variability profile basedupon a mathematical model of the plurality of pressure readings at eachcross-directional position.
 21. The method of claim 18, furtherincluding: adjusting the sensing roll to reduce the variability of thepressure profile.
 22. A method for sensing and removing the effects ofrotational variability from the nip pressure profile of a sensing rollof a nip press, comprising: placing multiple sets of sensors on thesensing roll, each sensor of the multiple sets of sensors being disposedaround the sensing roll for sensing pressure exhibited on the sensingroll at that sensor's location and for providing a pressure signalrepresentative thereof, each of the sensors of the multiple sets beingdisposed a particular cross-directional position along the sensing roll,each sensor of the multiple sets having a corresponding sensor in theother sets which is located at the same cross-directional position andis spaced apart circumferentially on the sensing roll; measuring thepressure exerted on each sensor of the multiple sets when the sensingroll is rotating and the sensors are in the nip region of the nip press;and comparing the pressure readings of each sensor of the multiple setswith the pressure readings of the corresponding sensors of theadditional sets of sensors.
 23. The method of claim 22, wherein thesensors of the plurality of sets are disposed along the sensing rollsuch that a sensor of the first set will be in the nip region of the nippress when a sensor of the second set is also in the nip region of thenip press.
 24. The method of claim 22, wherein a pressure measurement ismade to each sensor of each sets as the sensors enter the nip region.25. The method of claim 22, wherein the measurements of the sensors aretransmitted wirelessly by a device attached to the sensing roll.
 26. Themethod of claim 22, wherein each sensor of the first set is located atdifferent cross-directional position from another sensor of the firstset.
 27. The method of claim 22, wherein: the first set of sensors andthe additional sets of sensors are disposed in a helical configurationalong the sensing roll and spaced apart circumferential from each otherevenly or unevenly spaced.
 28. The method of claim 22, further includingadjusting the sensing roll to reduce the variability of the nip pressureprofile.
 29. The method of claim 22, wherein: the first set of sensorsare disposed along the sensing roll in a particular pattern and theadditional sets of sensors are disposed in the same pattern.
 30. Amethod for sensing and removing the effects of rotational variabilityfrom the nip pressure profile of a sensing roll of a nip press,comprising: providing a sensing roll having a working length and aplurality of cross-directional positions disposed along the workinglength; placing multiple pressure-measuring sensors at eachcross-directional position, the plurality of sensors being spaced apartcircumferentially from the other; measuring the pressure exerted on eachsensor at each cross-directional location as the sensor moves into thenip region of the nip press; averaging the pressure measurements fromeach sensor of a pair to determine an average pressure measurement ateach cross-directional position; and utilizing the average pressuremeasurements from each cross-directional position to provide a nippressure profile for the nip press.
 31. The sensing roll of claim 1,wherein the at least one additional set of pressure-measuring sensorsincludes a second set and a third set, wherein each sensor of the firstset has a corresponding sensor in the second and third sets which islocated at the same cross sectional position but is spaced 120° apartcircumferentially, each set of sensors forming a partial helix whichextends about 120° around the sensing roll.
 32. The sensing roll ofclaim 1, wherein the at least one additional set of pressure-measuringsensors includes a second set, wherein each sensor of the first set hasa corresponding sensor in the second set which is located at the samecross sectional position but is spaced 180° apart circumferentially,each set of sensors forming a partial helix which extends about 180°around the sensing roll.
 33. The sensing roll of claim 1, wherein the atleast one additional set of pressure-measuring sensors includes a secondset, a third set and a fourth set, wherein each sensor of the first sethas a corresponding sensor in the second, third and fourth sets, eachcorresponding sensor being located at the same cross sectional positionbut is spaced 90° apart circumferentially from an adjacent sensor, eachset of sensors forming a partial helix which extends about 90° aroundthe sensing roll.
 34. The sensing roll of claim 1, wherein the at leastone additional set of pressure-measuring sensors includes n sets ofsensors, wherein each sensor of the n sets has a corresponding sensor inthe remaining n sets, each corresponding sensor being located at thesame cross sectional position but is spaced 360°/n apartcircumferentially from an adjacent sensor, each set of n sensors forminga partial helix which extends about 360°/n around the sensing roll.